[pschanely]

Thank you. And, heck yes, more people need to be talking about how to deal with computations that are largely repeated. That problem comes up all over the place.

Couchdb had an interesting approach for this that did not require inverses: they persist intermediate reduce results, so that you can re-use nodes in the tree that haven't changed. So clever. http://horicky.blogspot.com/2008/10/couchdb-implementation.h...

[btown]

Database indices (SQL and no) are similar in that regard - they are persisted so that a single insertion or update does not invalidate the entire index. Cache invalidation is a hard general problem, but easier when a closed system (like a database) is the only thing using its own cache, and the interface is much higher level.